docs: def deltas(errors, epsilon, mean, std):
      """Compute mean and std deltas.
  
      delta_mean = mean(errors) - mean(all errors below epsilon)
      delta_std = std(errors) - std(all errors below epsilon)
      """
      below = errors[errors <= epsilon]
      if not len(below):
          return 0, 0
  
      return mean - below.mean(), std - below.std()